This application claims, under 35 USC 119, priority of Japanese Application No. 2001-154386 filed May 23, 2001.
(1) Field of the Invention
The present invention relates to an intercom system for a building or an apartment house, and more particularly to an intercom system for a building or an apartment house which can achieve power saving by suppressing current consumption and, at the same time, can ensure favorable talking quality by preventing the occurrence of howling.
(2) Description of the Related Art
A conventional intercom system for a building or an apartment house has a structure as shown in a block diagram of FIG. 3.
The intercom system for a building or an apartment house shown in the drawing has at least one main entrance station 101, a plurality of residential master stations 102, 102, . . . which are respectively installed inside of a plurality of residences in a building or an apartment house, a common line 103 connecting the main entrance station 101 and respective residential master stations 102, 102, . . . in parallel, a line power supply 104 for supplying a direct current power supply (DC power supply) to the main entrance station 101 and respective residential master stations 102, 102, . . . in parallel through the common line 103, an electronic door lock 105 which is connected to the main entrance station 101 for locking and releasing an entrance door of a the building or apartment house, and a plurality of call switches 106, 106, . . . which are connected to respective residential master stations 102, 102, . . . and are mounted on front doors of respective residences (hereinafter referred to as xe2x80x9cresidential front doorsxe2x80x9d) for operation by a visitor to the residence.
In the drawing, the main entrance station 101 comprises a talk module 110 which includes a control circuit 120, a line impedance and voltage regulating circuit 121, a multiplex/separation circuit 122, a speech circuit 123, a data transmission/reception circuit 124, an electric door lock circuit 125, an electric door drive circuit 126 and a power supply circuit 127, and at least one switch module 111 which includes a control circuit 130, a call switch 131, and a lighting circuit 132.
Further, each residential master station 102, 102, . . . includes a control circuit 140, a line impedance and voltage regulating circuit 141, a multiplex/separation circuit 142, a speech circuit 143, an electric door lock releasing button 144, a data transmission/reception circuit 145 and a power supply circuit 146.
Further, the line power supply 104 includes a power supply circuit 150 and a choke circuit 151.
In the intercom system for a building or an apartment house having such a structure, the choke circuit 151 of the line power supply 104 supplies stabilized direct current power such as DC 24 V, for example, to the common line 103 from the power supply circuit 150. This direct current power is supplied as standby operational power to the power supply circuit 127 through the line impedance and voltage regulating circuit 121 of the talk module 110 of the main entrance station 101 and to the power supply circuits 146 through the line impedance and voltage. regulating circuits 141 of respective residential master stations 102, 102 When a visitor standing at the entrance of the building or apartment house operates the call switch 131 of the switch module 111 of the main entrance station 101 to call a resident living in a specified residence, a calling data signal is output from the control circuit 130 in response to operation of the call switch and is transmitted to respective residential master stations 102, 102, . . . through the control circuit 120, the data transmission/reception circuit 124, the multiplex/separation circuit 122 of the talk module 110 and the common line 103.
In respective residential master stations 102, 102, . . . , the control circuit 140 compares an address which forms the calling data signal which is received through the common line 103, the multiplex/separation circuit 142 and the data transmission/reception circuit 145 with a preset address at its own terminal. If these addresses agree with each other, the control circuit 140 generates a calling tone by means of a speaker (not shown in the drawing) in the speech circuit 143 so that the resident in the called residence is informed of the call from the visitor standing at the entrance of the building or apartment house.
Upon hearing the calling tone generated by the speaker (not shown in the drawing) in the speech circuit 143 of the residential master station 102, the resident living in the called residence of the building or apartment house picks up a handset (not shown in the drawing) in the speech circuit 143. The control circuit 140 detects this pick up of the handset to activate the speech function (detailed explanation thereof being omitted) of the speech circuit 143 and to transmit a response data signal to the talk module 110 of the main entrance station 101 through the data transmission/reception circuit 145, the multiplex/separation circuit 142 and the common line 103.
In the speech module 110 of the main entrance station 101, the control circuit 120 detects the response data signal which is received through the common line 103, the multiplex/separation circuit 122 and the data transmission/reception circuit 124 and activates the speech function (detailed explanation thereof being omitted) of the speech circuit 123. Accordingly, a speech path (detailed explanation being omitted) is established between a microphone and a speaker (not shown in the drawing) which form the speech circuit 123 and the handset (not shown in the drawing) of the speech circuit 143 of the residential master station 102 to enable transmitting and receiving speech signals through this speech path.
Subsequently, when the resident living in the called residence operates the electric door lock releasing button 144 of the residential master station 102 for releasing the electric door lock 105 mounted on the front door at the main entrance, a release data signal is output from the control circuit 140 and is transmitted to the control circuit 120 of the talk module 110 of the main entrance station 101 through a path similar to the path for the above-mentioned response data signal.
Further, the control circuit 120 of the talk module 110 of the main entrance station 101 detects the lock release data signal transmitted from the residential master station 102 and controls the electric door lock drive circuit 126 so as to drive the electric door lock circuit 125 to release the electric door lock 105.
However, in the conventional intercom system for a building or an apartment house, the choke circuit 151 of the line power supply 104 has given frequency characteristics and hence, when the speech signals for establishing the talk are transmitted to the common line 103, the frequency characteristics of the choke circuit 151 cause feedback of the speech signals so that it is difficult to cancel the feedback speech signals at the speech circuit 123 of the talk module 110 in the main entrance station 101 and at the speech circuit 143 of the called residential master station 102 whereby there exists a drawback that howling can be generated.
Further, in the line impedance and voltage regulating circuit 121 of the talk module 110 which forms the main entrance station 101 and in the line impedance and voltage regulating circuits 141 of respective residential master stations 102, 102, . . . , the power supply voltage from the line power supply 104 is set to a high value to ensure a dynamic range with a standby current value. At the same time, the electric door lock circuit 125 of the talk module 110 in the main entrance station 101 is driven at a stabilized low-level voltage through the electric door lock drive circuit 126 by the control circuit 120 so as to lock and release the electric door lock 105. Accordingly, there is a drawback that the current consumption is increased in the talk module which is operated by voltage stabilized through the power supply circuit 127, for example DC 5 V.
Further, when the call switch 106 mounted at the residential front door or the call switch 131 at the main entrance is operated, the calling tone is generated by the speaker (not shown in the drawing) in the speech circuit 143 controlled by the control circuit 140 of the residential master station 102 detecting the calling operation. Accordingly, current consumption is increased in the residential master station operated by voltage stabilized through the power supply circuit 146, for example DC 5 V.
The present invention has been made to solve the above-mentioned drawbacks and it is an object of the present invention to provide an intercom system for a building or an apartment house which can achieve the power saving by suppressing current consumed at the time of calling initiated by a visitor standing at a main entrance of a building or an apartment house or a residential front door or at the time of releasing an electric door lock mounted on a front door of the main entrance of the building or apartment house and, at the same time, can ensure the favorable talk quality by suppressing howling.
To achieve the above-mentioned object, an intercom system for a building or an apartment house according to the present invention includes at least one main entrance station with a talk module for calling and talking and at least one switch module connected to the talk module and having a call switch for selecting a residential station, a line power supply for supplying power to a common line, a plurality of residential master stations for receiving calls and talking with the main entrance station on the common line in parallel. The line power supply includes a choke circuit for increasing an AC impedance to a high impedance, the talk module of the main entrance station includes a speech circuit having a load resistance which is connected to the common line, and each residential master station includes a speech circuit having a load resistance which is connected to the common line. Further, in the intercom system for a building or an apartment house of the present invention the choke circuit of the line power supply is provided with a frequency response leveling circuit.
According to the intercom system for a building or an apartment house having such a structure, by connecting the speech circuits having the load resistances in series with the line impedance and voltage regulating circuit of the talk module which forms the main entrance station and the line impedance and voltage regulating circuits of respective residential master stations which are connected to the common line in parallel, it becomes possible to sufficiently cancel the feedback tone signals without receiving the influence of the alternating current impedance which the common line has so that the generation of howling can be prevented.
Further, in the intercom system for a building or an apartment house of the present invention, the talk module of the main entrance station and the residential master stations are respectively provided with line impedance and voltage regulating circuits for increasing input impedance at the standby state to a high impedance and the line impedance and voltage regulating circuits are respectively provided with fixed voltage circuits.
According to the intercom system for a building or an apartment house having such a structure, when the main entrance station and the residential master stations receive the direct current power from the line power supply, the line impedance and voltage regulating circuits respectively perform constant-current operations due to controls performed by the fixed voltage circuits and hence, even when the main entrance station, the residential master station and the line power supply are connected to the common line in parallel, the lowering of the alternating impedance to the common line is prevented.
According to the intercom system for a building or an apartment house having such a structure, an AC impedance in a high range is suppressed by the frequency response leveling circuit which is connected to the choke circuit of the line power supply in parallel and hence, even when the frequency to the direct current power supply becomes high, the AC impedance to the common line is only increased up to a given impedance.
Further, in the intercom system for a building or an apartment house of the present invention, the talk module of the main entrance station compnrises a constant-current electric door lock drive circuit for driving an electric door lock circuit which locks and releases an electric door lock.
According to the intercom system for a building or an apartment house having such a structure, the power supply to the constant-current electric door lock drive circuit of the talk module of the main entrance station can be performed such that, without using a low-level voltage which is stabilized in the talk module, the constant-current is a small current value is supplied from the common line so as to drive the electric door lock circuit thus locking and releasing the electric door lock whereby the power saving can be achieved.
Further, each residential master station of the intercom system for a building or an apartment house of the present invention comprises a piezoelectric element circuit which generates a calling tone upon operation of a call switch which is installed at a residential front door.
According to the intercom system for a building or an apartment house having such a structure, the power supply to the piezoelectric element circuit of the residential master station which informs of the operation of the call switch with the generation of call tone can be performed such that, without using a low-level voltage which is stabilized in the residential master station, the constant-current to be a small current value is supplied based on the direct current power supply from the common line so as to drive the piezoelectric element circuit whereby the power saving can be achieved.